Alterations in the viscoelastic properties of the myocardium, ventricular interaction through the septum, incomplete relaxation rate, the pericardium, the lungs, and changes in pleural pressure are among the mechanical factors that may affect cardiac function. We will use closed and open-chest dogs whose hearts have been outlined with small coils of tantalum wire inserted with a steerable catheter without opening the chest or thorax, and pressure measurements with catheter-tipped pressure transducers to assess the relative contribution of these and other factors to changes in the heart's diastolic and systolic function in normal and ischemic hearts. This experimental work will complement theoretical studies on the potential importance of these and other factors in determining cardiac function. Other work will center on deriving better methods to describe the deformation of the heart as a whole, with subsequent experimental validation and use in describing how altering the external constraints on the heart by much maneuvers as opening the chest, alter cardiac position and dynamic geometry. Preliminary work suggests that it is possible to compute the pleural pressure at the level of the heat from the diastolic pressures in the two ventricles. We will extend this work and complete a direct experimental validation of the equations used for this computation.